The Skegness HST started in Summer 2009 I believe with 2 round trips starting from Nottingham. This was cut back to a single round trip in 2010 and started from Derby. I remember riding on a round trip from Skegness in 2009, and it was a 30mph stagger all the way from Skegness to Boston, with a couple of 5mph restrictions over some bridges. When I saw a HST on the branch at Havenhouse last year, it passed at linespeed (50mph), so the 30mph restriction for locos has at least been removed in places (or may be just a case for HST's). This year could see the whole line being back up to linespeed thanks to the track renewals.
By the sound of things that line must have some of the oldest track on the network. Even at 50 mph I can't see this being competitive with road transport.
I believe there have been further enhancements to the Poacher line, which will allow the HST services to run at line speed for more of the journey. Can anyone confirm this?